Inorg. Chem. 1990, 29, 3952-3954
3952
Table 111. Atomic Parameters Used in the Calculations atom orbital H,,, eV tIn CI Ta 6s 2.28 -10.1 -6.86 2.24 6P 5d -12.12 4.76 1.94 0.6815 Fe 4s -8.40 1.90 -5.00 1.90 4P 5.35 2.00 0.5505 3d -12.2 Te 5s -20.8 2.51 -13.2 2.16 5P Si 3s -17.3 I .38 3p -9.20 1.38
C2
0.6815 0.6815
"Exponent in the double ( function for d orbitals. in the Ta4TedSi chain and is, by our calculations, to be attributed to the Ta 5d Orbitals' The Ta-Si bonding states are localized to a small energy interval. It is this bonding that greatly stabilizes the chain structure. The compound is expected to be metallic, with the conduction bands being largely made up of Ta 5d states. The staggered or antiprismatic form is more stable than -the eclipsed one. While pairing of the interstitial atoms is in principle possible, it depends on the valence electron count. For
a system with 96 electrons, as in Ta4Te4Si,the pairing distortion is not favored. An overlap population analysis indicates that replacing Si by Fe is quite feasible. The Fe compound thus obtained should again be conducting; the states around the Fermi level are now largely Fe 3d. Oxidation is more likely to take place than reduction, more so with the Fe compound than the Si compound. Acknowledgment. We are grateful to the National Science Foundation for its generous support through Grant CHE 8912070. We thank Jane Jorgensen and Elisabeth Field for the drawings. Appendix The extended Hiickel tight-binding methodw is used throughout the Daoer. A summarv of the atomic Darameters is given in Table 111.' Atomic distances used in both structures, T
